Shouldn't the sentence "Therefore it appears that the Maya were comfortable with one Haab month falling in midsummer at one point, but falling in midwinter thousands of years later." really be "… but falling in midwinter 730 years later."?
Reasoning: The calendar did not use leap days, and therefor had an inaccuracy of roughly one day in four years. To shift a particular day of the Haab from midsummer to midwinter, a shift of half a year or 182.5 days, should take 4*182.5 or 730 years.